linux-kernel - Re: [PATCH v7 10/45] x86/sev: Add support for hypervisor feature VMGEXIT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <453e1ccd-50c6-d6c9-e4e8-49fff6382101@amd.com>
Date:   Mon, 6 Dec 2021 09:15:59 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v7 10/45] x86/sev: Add support for hypervisor feature
 VMGEXIT



On 12/2/21 11:52 AM, Borislav Petkov wrote:
> On Wed, Nov 10, 2021 at 04:06:56PM -0600, Brijesh Singh wrote:
>> +/*
>> + * The hypervisor features are available from GHCB version 2 onward.
>> + */
>> +static bool get_hv_features(void)
>> +{
>> +	u64 val;
>> +
>> +	sev_hv_features = 0;
>> +
>> +	if (ghcb_version < 2)
>> +		return false;
>> +
>> +	sev_es_wr_ghcb_msr(GHCB_MSR_HV_FT_REQ);
>> +	VMGEXIT();
>> +
>> +	val = sev_es_rd_ghcb_msr();
>> +	if (GHCB_RESP_CODE(val) != GHCB_MSR_HV_FT_RESP)
>> +		return false;
>> +
>> +	sev_hv_features = GHCB_MSR_HV_FT_RESP_VAL(val);
>> +
>> +	return true;
>> +}
> 
> I still don't like this.
> 
> This is more of that run-me-in-the-exception-handler thing while this is
> purely feature detection stuff which needs to be done exactly once on
> init.
> 
> IOW, that stanza
> 
>          if (!sev_es_negotiate_protocol())
>                  sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_PROT_UNSUPPORTED);
> 
> should be called once in sev_enable() for the decompressor kernel and
> once in sev_es_init_vc_handling() for kernel proper.
> 

I will look into it, I will improve the sev_enable() to call GHCB MSR 
protocol query the version and feature.


> Then you don't need to do any of that sev_hv_features = 0 thing but
> detect them exactly once and query them as much as you can.
> 
> Thx.
>